what exactly is pcsa_force (from ligaments' properties)

Mary K · Post by **Mary K** » Thu Jul 17, 2014 4:54 pm

Hi there!
i want to create my own cruciate ligament but I cannot understand what this property exactly is:

OpenSim_DECLARE_PROPERTY (pcsa_force, double,"force magnitude that scales the force-length curve")

(from the source code)

When I google "PCSA force" I find nothing, but only PCSA which is not a force but "physiological cross-sectional area" (from wikipedia).

Does anyone know more about the "pcsa_force"?

Thanks!

jimmy d · Post by **jimmy d** » Mon Jul 28, 2014 9:31 pm

Hi Maria,

The maximum isometric force for a muscle can be estimated from measured PCSA and a specific tension of 61 N/cm2. So even though PCSA is not a force, it is related to the force a muscle can produce.

Modeling ligaments are analogous to muscles without active components. Therefore PCSA can be used to scale the force-length curve of a ligament.

Cheers,
-James

Mary K · Post by **Mary K** » Thu Sep 04, 2014 11:01 am

Hi James,
thanks for responding!

Maybe you could answer my question here: https://simtk.org/forums/viewtopic.php?f=91&t=5097
(it's seems that the function bool Ligament::setMaxIsometricForce(double aMaxIsometricForce) sets the same value to the parameter 'pcsa_force': set_pcsa_force(aMaxIsometricForce);. (Why?!)

The maximum isometric force for a muscle can be estimated from measured PCSA and a specific tension of 61 N/cm2.

When I study papers to find average measured parameters of ligaments (like length, strain etc) I don't ever find something like 'measured PCSA parameter'

Is there any possibility that the force-length curves found in the bibliography have already customized the results according to the pcsa_force parameter? So we can just set pcsa_force=1?

EDIT: In this paper there are measured values for cruciate ligaments' PCSA (mm^2). http://www.sciencedirect.com/science/ar ... 094900280#

jimmy d · Post by **jimmy d** » Thu Sep 11, 2014 2:14 pm

Hi Maria,

That ligament code if pretty old and based off of muscle, hence the naming conventions. Even the idea of a max isometric force for a ligament is flawed. It appears this value just scales the related curves.

If you want to view the behavior, I would put ligaments on a model, adjust the parameters, and view the curves directly in the GUI.

The ligament class is on the development notes for a future release.
-james

what exactly is pcsa_force (from ligaments' properties)

what exactly is pcsa_force (from ligaments' properties)

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